1. Field of the Invention
The present invention relates a focus detection apparatus used in an image pickup apparatus such as a digital camera or a video camera.
2. Description of the Related Art
Japanese Patent Laid-open No. S58-24105 discloses a focus detection apparatus which performs focus detection of a pupil division method by using a two dimensional image sensor (an image pickup element) in which a micro lens is formed for each pixel. In the focus detection apparatus disclosed in Japanese Patent Laid-open No. S58-24105, a photoelectric converter of each pixel constituting the image sensor is divided into a plurality of photoelectric conversion portions, and the divided photoelectric conversion portions receive light beams passing through different regions from each other in a pupil of an imaging optical system via one micro lens.
Japanese Patent Laid-open No. 2005-106994 discloses an image pickup apparatus which performs focus detection of a pupil division method by using a CMOS sensor as an image pickup element. In the image pickup apparatus disclosed in Japanese Patent Laid-open No. 2005-106994, a portion of pixels among a plurality of pixels which constitute the CMOS sensor include divided photoelectric conversion portions in order to detect a focus state of an image pickup optical system (an imaging optical system). The divided photoelectric conversion portions receive light beams passing through different regions from each other in a pupil of an image pickup lens via one micro lens.
In conventional arts, an added signal of a plurality of pixels sharing one micro lens is used as an image signal. By configuring so that a charge can move between the plurality of pixels, deterioration in image quality due to charge saturation can be reduced. However, when performing focus detection by using pixel signals of a plurality of pixels, it is difficult to obtain an accurate focus detection result because a charge moves between a plurality of pixels in a case where incident light amount is large (in a high luminance state). That is, if a charge movement (a charge transfer) occurs, a phase difference which is smaller than a phase difference ought to be observed is detected. Therefore, a focus detection error is large, which leads to deterioration in focus accuracy and delay in focusing operation.